1. Field of the invention:
This invention relates to a method for the production of semiconductor laser devices, especially those having a buried heterostructure therein.
2. Description of the related art:
Semiconductor laser devices, which comprise a buried heterostructure resulting from surrounding the active layer for laser oscillation with a heterojunction, have excellent device characteristics in that provide for stabilized laser oscillation which can be attained in a transverse mode and a low oscillation threshold current level which can be maintained, and thus they are usable as laser light sources.
In a conventional semiconductor laser device having a structrue such as that shown in FIG. 2, in which a p type crystal 10 is employed as a substrate for epitaxial crystal growth, the p-n junction of a current confining region has to withstand voltage at a high level, so that a high output power operation can be achieved by the application of a high voltage. This conventional semiconductor laser device is produced as follows: On the p-InP substrate 10, a p-InP buffer layer 20, a non-doped InGaPAs active layer 30, and an n-InP cladding layer 40 are successively grown by liquid phase epitaxy. Both sides of the resulting multi-layered crystal structure are then etched in a manner to reach the buffer layer 20. On the post-etched portion, an n-InP current blocking layer 50 and a p-current confining layer 60 are grown as burying layers. According to the structure of the above-mentioned device, in order to block the electroconductivity between the cladding layer 40 and the current blocking layer 50, the top of the current blocking layer 50 must be positioned below the active layer 30. For this reason, both the depth of etching in the multi-layered crystal structure and the growth thickness of the current blocking layer 50 must be regulated with high precision. However, neither liquid phase epitaxy nor a wet-etching technique can attain such precise regulation, resulting in a low production yield of semiconductor laser devices of this type.